Most of the fluid media used in the processing industry involve oil and gas streams of different corrosive grades. These flow conditions, including medium flow, are considered to be either clean, dirty, or worn (in slurry conditions). The main difference is the quantity and type of suspended solid particles that cause valve blockage or corrosion damage. In addition, medium streams containing sulfur and other mixtures will help to form a corrosive environment when combined with high temperatures. For such medium flow, the valve shall have sufficient service life by carefully selecting materials. Corrosion engineers continue to research and develop materials to solve these problems.

1、 Special valves for oil refining hydrocracking and coking units

The refinery delayed coking unit is a processing process of deep thermal cracking of vacuum residue to generate gas, light distillate oil and coke. It is an important means for refineries to improve the yield of light oil and produce petroleum coke. The process is divided into coking and decoking. Coking is continuous production and decoking is intermittent production. The inlet and outlet of heating furnace and coke tower are connected by four-way valve. The four-way valve is an important channel for switching the heating furnace into the coke tower. It is a special valve, which is used in high temperature occasions. Its quality directly affects the production capacity of the device. Both new designs and old devices in China mostly use imported four-way plug valves, but the price is expensive. However, the domestic four-way valve generally has the problems of unreasonable structure, unstable quality and easy failure.

Hydrocracking in refineries is one of the main crude oil refining processes. As the hydrocracking unit operates under high temperature and pressure, the medium is flammable and explosive hydrogen and hydrocarbons, and the working condition is special, so the seal must be reliable. Therefore, higher requirements are put forward for the design and structure of the valve. At present, most domestic stainless steel wedge gate valves and direct flow globe valves are used.

2、 Oil gas special valve

In order to control the oil and gas flow, the special oil and gas valve shall have the following basic properties: sealing, pressure resistance, safety, adjustability, fluid flow and switching flexibility. For high pressure, flammable and explosive oil and gas medium, the sealing shall be solved first, and the special working condition requirements of oil and gas special valves shall be considered:

① In wet natural gas containing hydrogen sulfide and carbon dioxide, special requirements are put forward for valve body material;

② Brine, residual acid and other corrosive media exist in the wellhead equipment and gathering and transportation system, and the selection of valve body materials and anti-corrosion requirements;

③ Dust and solid particles speed up the flushing and abrasion of the valve closing parts, which makes the sealing pair fail quickly;

④ In the outdoor of plateau, desert and alpine region, the valve material is brittle at low temperature, bending deformation, etc;

⑤ The special valves for oil and gas on long-distance transmission pipelines shall have the same service life as the pipelines and shall not be replaced for decades.

All these indicate that the special oil and gas valve is different from the ordinary valve. It should have high reliability under harsh conditions and meet the requirements of high strength and no leakage.

3、 Chlorine working condition

The selection of valves under chlorine containing conditions shall refer to the Dry Chlorine Pipeline System prepared by the American Chlorine Institute.

The working condition containing chlorine or liquid chlorine is highly corrosive, especially the working condition containing water. HCl (hydrochloric acid) formed by mixing chlorine and water will corrode the valve body and internals. Because chlorine has a high coefficient of thermal expansion, if liquid chlorine is sealed in the valve cavity, the pressure in the valve cavity will increase at a high speed. The valve used in this condition shall have a reliable middle chamber pressure relief function.

4、 Refrigeration (low temperature) working condition

Although the valves for low temperature service are based on ASME B16.34 and API standards, these valves also have other design functions to ensure reliable operation in low temperature service. Such a valve may also include a bonnet extension design that extends the distance between the packing and the operating mechanism and the cryogenic fluid, thus allowing the stem packing to be operated at a higher temperature and ensuring that the valve operating device will not be frozen in use. MSS SP-134 provides some details that include the bonnet extension design.

5、 Hydrofluoric acid working condition

Valves used in hydrofluoric acid service should only be limited to the types of valves that have been demonstrated in use or can successfully handle this condition in testing. Valves that do not normally provide an opportunity for solid material accumulation are the preferred valve type. The hydrofluoric acid treatment operation shall be carried out by technicians with qualification certificates who strictly control the listed valves. The design, material requirements and internal geometry details of these valves (typical carbon steel valves with special monel trim or solid monel trim) are very detailed. This valve should be designed as a special structure resistant to hydrofluoric acid corrosion. Under hydrofluoric acid working conditions, the inspection and test of valves shall be higher than the standard used for typical process valves.

6、 Hydrogen working condition

The valves used in this kind of working condition are usually of high casting quality compared with conventional casting products. Because hydrogen is a highly permeable fluid, welded connection valves with a pressure rating greater than or equal to 600 pounds reduce potential sources of leakage in use.

API 941 covers the selection and application range of materials in hydrogen service.

7、 Oxygen working condition

When applicable, valves used in oxygen containing service shall comply with CGA G4.4-2003 Oxygen Piping System. Valves used in this condition should be completely degreased, clean, installed under clean conditions, properly packaged and sealed, because oil and grease are extremely flammable in the presence of oxygen. Relevant guidelines are given in CGA G4.1 Cleaning Equipment under Oxygen Conditions. Proper handling and storage is necessary prior to installation.

Bronze or Monel valve body and internal materials suitable for oxygen containing working conditions are often used to prevent sparks and ignition due to high-energy mechanical collision. Silicon based grease with special preparation is used in oxygen containing working conditions, because standard hydrocarbon lubricating oil should not be used in the presence of oxygen.

8、 Pulsating or unstable flow

The check valve used in pulsating or unstable flow shall be selected with special consideration. For example, the check valve used in reciprocating compressor may be quickly opened and closed with the change of flow, which may lead to hammering and valve damage. There may be different opinions on the types of valves used in pulsating and unstable flow, but generally butterfly check valves, swash plate check valves and axial flow check valves are recommended for pulsating or unstable flow.

9、 Acid containing working condition (wet H2S working condition)

The use of valve materials in sour service shall comply with NACE MR0103 standard. This standard for the downstream hydrocarbon processing industry limits the hardness of all steels; Austenitic steel solution annealing is required; It is prohibited to use certain materials for pressure parts (including valve stem); And put forward special requirements for bolted connection and welded valves.

Attention should be paid to the user's responsibility in NACE MR0103, which stipulates that the user should specify whether to expose the bolt to H2S containing environment. Unless otherwise specified by the user, bolts not inside the valve, such as bonnet connecting bolts, often comply with the product standard, and sulfur working conditions are not included in this standard. If the bolting material does not directly withstand the process fluid, the body bonnet bolting does not need to meet NACE requirements. If any sulfur leakage from sulfur containing oil products cannot be eliminated or evaporated (such as block valve), the bolted connection shall comply with NACE standard.

If materials allowed by NACE are considered unnecessary, special attention should be paid to bolting materials. This imposed hardness requirement will result in a reduction in strength. The strength of bonnet connecting bolts will be reduced and may not be suitable for the same design conditions as standard bolting materials.

10、 Viscosity or curing conditions

For valves used in viscous or solidified fluid conditions, such as liquid sulfur or heavy oil, in order to make the valve operable, steam tracing or steam casing is often required to maintain sufficient operating temperature. Special attention should be paid to check valves because their hysteresis will cause operational problems.